Combination catalytic reformingthermal reforming process



United States atentO COMBINATION CATALYTIC REFORMING- THERMAL REFORMING PROCESS George R. Donaldson, North Riverside, 111., assignor, by mesne assignments, to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware Application May 26, 1955, Serial No. 511,293

2 Claims. (Cl. 208-64) This invention relates to the catalytic conversion of hydrocarbons boiling within the gasoline range. It is more specifically concerned with a novel combination ofcatalytic reforming, solvent extraction and thermal reforming.

The recent developments in the automotive industry have increased the demand for high octane numbered gasolines and the petroleum industry has been striving to keep up with these demands. One process that has achieved great commercial acceptance is the catalytic reforming process. The term reforming is well known in the petroleum industry and refers to the treatment of gasoline fractions to improve the anti-knock characteristics thereof. A highly successful and economical reforming process is described in U.S. Patent No. 2,479,110, issued to Vladimir Haensel. However, the present reforming processes are all limited by decreasing yields at increasing octane numbers. There are also other limitations. For example, when a full boiling range straightrun gasoline or a relatively wide boiling range naphtha is reformed in the presence of a catalyst that promotes dehydrogenation of naphthenes, dehydrocyclization of paraffins and hydrocracking of paratfins, relatively poor yields and considerable fouling of the catalyst are obtained when the operating conditions are selected to obtain large octane number appreciation. This apparently is due to the fact that the relatively severe operating conditions that must be maintained in order to satisfactorily upgrade the higher boiling parafiinic constituents of the feed are too severe for some of the other constituents. The result is that an appreciable part of the feed stock is unnecessarily. converted to gases and to catalyst carbon. I have invented a process which largely overcomes these objectionable features of the prior art reforming processes.

It is an object of the present invention to reform a full boiling range straight-run gasoline, or a relatively wide boiling fraction thereof, in such a manner that increased yields of reformate and longer catalyst life are obtained while producing a liquid product of the desired quality.

It is another object of the present invention to provide an improved combined operation which will effect an improvement in octane number from the straight chain or branched .chain paratfins in the charge stock.

In one embodiment the present invention relates to a process which comprises subjecting hydrogen and a gasoline fraction to reforming in a reforming zone, introducing at least a portion of the effluent from said reforming Zone to a separation zone, separately withdrawing from said separation zone a predominantly aromatic fraction and a predominantly paraffinic fraction, introducing at least a portion of said predominantly paraflinic fraction to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling fraction and a low boiling fraction, and subjecting at least a portion of said low boiling fraction to a thermal treatment to convert a substantial portion of the parafiins in the fraction to olefins and recovering the efiluent.

In another embodiment the present invention relates to a process which comprises subjecting hydrogen and a mixture of a gasoline fraction and a high boiling p-araflinic recycle stock, prepared as hereinafter specified, to reforming in a catalytic reforming zone, stabilizing the reformate by removing normally gaseous components therefrom, introducing at least a portion of the stabilized reformate to a separation zone, separately withdrawing from said separation zone a predominantly aromatic fraction and a predominantly paraffinic fraction, introducing at least a portion of said predominantly paraffinic fraction to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling fraction and a low boiling fraction, recycling at least a portion of said high boiling fraction to said reforming Zone as said high boiling paraffinic recycle stock, passing at least a portion of said low boiling fraction to a thermal reforming zone and therein subjecting said fraction to a high temperature in the absence of a catalyst for a time sufficient to convert a substantial portion of paraflins to olefins and recovering the efiluent. v v p I v In a specific embodiment the present invention relates to a process which comprises subjecting hydrogen, a gasoline fraction and a high boiling raflinate fraction prepared as hereinafter set forth, to reforming in a reforming zone at a temperature of from about 600 F. to about 1000 F., in .the presence of a catalyst comprising alumina, platinum, and combined halogen, fraetionating the refermate to remove normally gaseous components therefrom, introducing the remaining fraction to a selective solvent extraction zone wherein the aromatics are separated from the paraffins, separately withdrawing from said selective solvent extraction zone a predominantly aromatic extract and a predominantly paraflinic raflinate, introducing said raffinate to a fractionation zone, separately withdrawing from said fractionation zone at least a high boiling rafiinate fraction and a low boiling ratfinate fraction, recycling at least a portion of said high boiling raffinate fraction to said reforming zone, introducing said low boiling rafiinate fraction to a thermal conversion zone and subjecting said fraction, in the absence of a catalyst, to a temperature within the range of from about 800 F. to about 1200 F., a pressure within the range of from about 50 to about 2000 pounds per square inch and for a period of time sufficient to convert a substantial portion of the parafiins in said stream to olefins, and recovering the effluent from said thermal conversion zone.

Briefly stated, my process comprises reforming a gasoline fraction in the presence of hydrogen. It is a preferred feature of my invention that a high boiling paraffinic recycle stock, prepared from the effluent from the reforming zone as hereinafter set forth, be recycled to the reforming zone. Hydrogen is separated from the reforming zoneeffluent and recycled to the reforming zone. The remaining liquid products are fractionated to stabilize the liquid, that is to reject the gaseous hydrocarbons produced in the process, and the resultant stabilized liquid is passed to a separation zone to separate the aromatics therefrom. It is preferred that the separation be performed in a selective solvent extraction zone. The predominantly paraflinic fraction from the separation zone is fractionated and a heavy fraction thereof is preferably recycled to the reforming zone. At least a portion of the low boiling portion of the predominantly parafiinic liquid fraction removed from the separation zone is subjected to a thermal conversion in the absence of a catalyst. The thermal treatment is at an elevated temperature and pressure to convert a substantial portion of the straight chain or slightly branched chain paraflins to olefins. In the thermal reforming zone additional aromatics are also formed, however in low amounts.

I have discovered, and my invention is based on this discovery, that the low boiling parafiins present in the eflluent from a catalytic reforming zone are not appreciably enhanced in octane number by subsequently treating these low boiling paraifins in a catalytic reforming zone. Therefore, it is not particularly advantageous or economical to catalytically reform the lower boiling parafiins by recycling them to the catalytic reforming zone. Therefore, when the effluent from a catalytic reforming zone is separated in a separation zone into a predominantly parafiinic fraction and a predominantly aromatic fraction, it is preferred to fractionate the predominantly parafiinic fraction into at least a low boiling fraction and a high boiling fraction and to catalytically reform only the higher boiling fraction, preferably by recycling the same to the catalytic reforming zone. I have discovered that the low boiling fraction may be markedly increased in octane number by a thermal con version or thermal reforming operation performed on this lower boiling fraction. The effiuent from the thermal reforming zone may be stabilized and combined with the aromatic-rich fraction from the separation zone to form a motor fuel of high octane number and excellent starting characteristics.

An additional feature of my process is that mild processing conditions may be employed in the catalytic reforming zone minimizing undesirable side reactions which otherwise reduce the yields of useful gasoline products. Reforming of the low octane number, high boiling paraflins in the raffinate by recycling these paraflins to the catalytic reaction zone results in their being dehydrocyclicized to aromatics and/or their being converted to lower boiling, high octane number parafiins without the excessive production of gaseous hydrocarbons that would result were these higher boiling parafiins substantially reacted in one pass in a reforming zone continued at cond tions of high severity. High severity single pass operation is also not desirable from considerations of the chemical equilibria involved, as in such single pass operations the aromatics present in the produet limit the extent to which such aromatics can be formed from naphthenes and paraffins. In contrast, however, the use of my process involves the removal of a substantial portion of the aromatics from the recycle charge to the reaction zone, which thus permits the formation of additional aromatics unrestricted by limitations of chemical equilibria.

The aromatics are separated from the parafi'ins and the naphthenes in the reformate for several reasons. One reason is that subsequent reforming in the presence of a high concentration of aromatics results in lower overall yields of reformate presumably due to the conversion of aromatics to gaseous hydrocarbons and/or to hydrocarbons boiling above the gasoline range. Another reason is that high concentrations of aromatics in the reaction zone tend to result in a greater carbon deposition and consequently a shorter process period. Still another reason, which has hereinbefore been mentioned, is that high concentrations of aromatics in the reaction zone tend to suppress the dehydrogenation of naphthenes to aromatics and to suppress the dehydrocyclization of paraffins to aromatics, said dehydrogenation and said dehydrocyclization being equilibrium reactions. By eliminating low octane number high boiling parafiins from the final product, the end product is a reformate of high 4 quality even though the charging stock has never been subjected to relatively severe operation conditions, as previously were necessary to produce high quality reformate.

However, in the reforming process the aromatics in the charging stock, or the aromatics formed in the reaction zone tend to react with each other, probably in a condensation or polymerization reaction to form heavy polynuclear aromatics. These heavy polynuclear aromatics are undesirable in the reaction zone since it is these materials which are the hydrocarbonaceous deposits, or which form the heavy carbonaceous deposits on the catalyst, which tend to deactivate the catalyst by coking the same. It is, therefore, preferred that these aromatics are removed from any recycle stock that is recycled to the reforming zone since otherwise these aromatics will readily react with each other in the reforming zone and deactivate and/or coke the catalyst.

As hereinbefore mentioned, I have discovered that the paraffinic fraction from a separation zone, particularly the raifinate from a selective solvent extraction zone, 15 not an entirely satisfactory material to recycle to a catalytic reforming zone since the lower boiling paraffins in the fraction are not substantially upgraded in octane number by subsequent catalytic reforming. I have also discovered that it is possible to thermally reform the lower boiling parafiins in the raflinate, thereby achieving substantfal increases in octane number. The higher boiling paraffins in the raffinate may be recycled to the catalytic reforming zone.

The charge stocks that may be reformed in accordance with my process comprise hydrocarbon fractions that boil within the gasoline range and that contain naphthenes and paraflins. The preferred stocks are those consisting essentially of naphthenes and parafi lns, although minor amounts of aromatics and even of olefins also may be present. This preferred class includes straight-run gasoline, natural gasoline and the like. The gasoline fraction may be a full boiling range gasoline having an initial boiling point within the range of from about 50 F. to about 100 F, and an end boiling point within the range of from about 350 F. to about 425 F., or it may be a selected fraction thereof which may be a higher boiling fraction commonly referred to as naphtha and having an initial boiling point within the range of from about 150 F. to about 250 F., and an end boiling point within the range of from about 350 F. to about 425 F. Mixtures of the various gasolines and/ or gasoline fractions may also be used and thermally cracked and/or catalytically cracked gasolines may also be used as charging stock, however, when these unsaturated gasoline fractions are used, it is preferred that they be used in admixture with a straight-run or natural gasoline fraction, or else hydrogenated prior to use as charging stock for my process.

The catalysts that may be used in the catalytic reforming zone of my invention comprise those reforming catalysts that promote dehydrogenation of naphthenic hydrocarbons and hydrocracking of parafi'inic hydrocarbons. Starting with a parafiinic hydrocarbon, from a yieldoctane standpoint it is preferable to upgrade the paraffinic hydrocarbon by dehydroeyclicizing the same to an aromatic than by cracking the parafiinic hydrocarbon. Since the recycle raffinate to the reforming zone consists prealumina, molybdena-alumina, chromia-alumina, and platinum on a cracking catalyst base may be used. As hereinbefore mentioned, it is preferred that the catalyst has substantial dehydrocyclicizing activity. I have found that catalysts of the platinum-alumina-combined halogen type, wherein the halogen content lies within the range of from about 0.1% to about 3% by weight of the final catalyst, especially those that contain about 0.01% to about 1% by weight of platinum and from about 0.1% to about 1% combined fluorine or those that contain about 0.1% to about 3.0% combined chlorine are especially effective and economical in my process because of the long life they exhibit, and also they promote isomerization reactions of both paraffins and naphthenes and paraflin dehydrocyclization reactions as well as the naphthene dehydrogenation and paralfin hydrocracking reactions.

The operating conditions maintained in the catalytic reforming step of my process should be such that substantial conversion of naphthenes to aromatics and relatively mild hydrocracking of paraffins are induced. Further the operating conditions should be such that there is substantial conversion of parafiinic compounds to aromatics by dehydrocyclization. It is also preferred that process conditions be used which result in only minor amounts of olefins being present in the product. When employing platinum-alumina-combined halogen catalyst the reforming process will be efiected at a temperature within the range of from about 600 F. to about 1000 F., pressure within the range of from about 50 to about 1000 pounds per square inch, and a weight hourly space velocity of from about 0.5 to about 20. It is preferred that the reforming reaction be conducted in the presence of hydrogen. The hydrogen present in the reaction zone will be within the range of from about 0.5 to about 20 mols of hydrogen. per mol of hydrocarbon.

The eflluent from the catalytic reforming zone is usually passed to a stabilizer which effects the separation of the normally gaseous material which comprises hydrogen, hydrogen sulfide, ammonia, and hydrocarbons containing from one to four carbon atoms per molecule, from the normally liquid hydrocarbons. A more concentrated aromatic fraction is then obtained in accordance with the present invention by subjecting the reformate, containing aromatic hydrocarbons, to a solvent extraction process.

The stabilizer liquid is then passed to a separation zone to produce a more concentrated aromatic fraction and to produce a predominantly paraffinic fraction. The separation of a more concentrated aromatic fraction may be accomplished in any conventional manner such as solvent extraction, solid absorption, fractional crystallization, mechanical separation, molecular sieves, extractive crystallization with urea, etc. However, the selective solvent extraction process is particularly preferred in the present invention since its use generally produces a raffinate most suitable for reforming.

Solvent extraction processes are used to separate certain components in a mixture from other components thereof by a separation process based upon a difference in solubility of the components in a particular solvent. It is frequently desirable to separate various substances by solvent extraction when the substances to be separated have similar boiling points, are unstable at temperatures at which fractionation is efliected, form constant boiling mixtures, etc. it is particularly desirable to separate aromatic hydrocarbons by solvent extraction because a petroleum fraction is normally a continuous mixture of hydrocarbons whose boiling points are extremely close together and because the petroleum fraction contains numerous cyclic compounds which tend to form constant boiling or azeotropic mixtures. As hereinbefore stated, the basis of a solvent extraction separation is the difference in solubility in a given solvent of one of the substances to be separated from the other. It may, therefore, be seen that the more extreme this difference, the easier the separation will be, and an easier separation reflects itself process-wise, in less expensive equipment and greater yields per pass in the use of processing equipment as well as in higher purity of product.

A particularly preferred solvent for separating aromatic hydrocarbons from non-aromatic hydrocarbons is a mixture of water and a hydrophilic organic solvent. Such a solvent may have its solubility regulated by adding more or less water. Thus, by adding more water to the solvent, the solubility of all components in the hydrocarbon mixture are reduced, but the solubility difference between the components is increased. This eifect is reflected processwise in less contacting stages required to obtain a given purity of product, however, a greater through-put of solvent must be used in order to obtain the same amount of material dissolved.

As hereinbefore stated, the solvent to be used in this invention is preferably a mixture of a hydrophilic organic solvent and water, wherein the amount of water contained in the mixture is selected to regulate the solubility in the solvent of the materials to be separated. Suitable hydrophilic organic solvents include alcohols, glycols, aldehydes, glycerine, phenol, amines, aminoalcohols, nitriles, sulfoxides, etc. Particularly preferred solvents are diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, tripropylene glycol, and mixtures thereof containing from about 1% to about 20% by weight of water. Other hydrophilic substances as sulfur dioxide, etc. may be used.

In classifying hydrocarbon and hydrocarbon type compounds according to increasing solubility in such a solvent, it is found that the solubility of the various classes increases in the following manner: the least soluble are the paralfins followed in increasing order of solubility by naphthenes, olefins, diolefins, cycloolefins, acetylenes,' sulfur, nitrogen, and oxygen-containing compounds and aromatic hydrocarbons. It may thus be seen that a charge stock which is rich in unsaturated compounds will present a greater problem in solvent extraction than a saturated charge stock since the unsaturated compounds fall between the parafiins and aromatics in solubility. It may be seen that an ideal charge to solvent extraction is one containing parafinic and aromatic hydrocarbons exclusively.

The parafiinic compounds also differ in their relative solubility in the solvent. The solubility appears to be a function of the boiling point of the paraffin, with the lower boiling or lighter paraflins being more soluble than the higher boiling or heavier paraffins. Therefore, when heavy paraflins are dissolved in the solvent, they may be displaced from the solvent by adding lighter paraflins thereto. In an embodiment of this invention it is preferred to recycle the heavier parafiins to the reforming zone and, therefore, a light paraffin is charged to the extraction zone to displace these heavier parafiins from the solvent by putting the heavier parafiins into the raflinate phase.

The predominantly paraffinic fraction from the separation zone, preferably the rafiinate from a solvent extraction zone, is subjected to a fractionation to fractionate the rafiinate into at least a high boiling fraction and a low boiling fraction. The raflinate may contain components which are high enough in octane number and low enough in boiling point so that they need not be enhanced in octane number and it is, therefore, preferred that a light fraction be fractionated from the raffinate and recovered as product or recycled to the solvent extraction zone as reflux on the extractor. Usually the isohexane and lighter fraction is not improved in octane number when thermally reformed and, therefore, it is preferred that the isohexane and lighter fraction be removed from the rafiinate before the light rafiinate is reformed in the thermal reforming zone. It is to be understood, however, that the isohexane and lighter fraction may be passed to the thermal reforming zone with the light fraction of the rafilnate that is to be thermally reformed. The raflinate from the extraction zone may also contain components which are heavier than are suitable for catalytic reforming and which may be removed by fractionation. For example, components boiling above about 425 F., and preferably above about 400 F. are generally not suitable for catalytic reforming since they tend to readily deactivate the catalyst. It is, therefore, preferred to separate the 400 F. and higher fraction by fractionation. Therefore, it is the fraction boiling within the range of from about normal hexane or at 156 F. to about 400 F. which is most suitable for reforming, and in accordance with the present invention the lower boiling fraction of this fraction is treated by thermal reforming while the higher boiling fraction of the fraction is preferably recycled to the catalytic reforming zone. The exact point at which the raflinate is divided into the lower boiling fraction and the higher boiling fraction will vary with the particular raflinate, however, generally the end point of the low boiling fraction will be within the range of from about 225 F. to about 325 F. The initial boiling point of the heavy fraction should correspond to the end point of the light fraction, that is it will generally be the same and will be Within the range of from about 225 F. to about 325 F.

As hereinbefore mentioned, the heavy portion of the rafiinate is preferably recycled to the catalytic reforming zone. The light portion of the rafiinate, that is the fraction having an end point within the range of from about 225 F. to about 325 F., is subjected to a thermal conversion in the absence of a catalyst. The thermal treatment is at a temperature, pressure and time sutlicient to convert a substantial portion of the parafiins in the light fraction of the raffinate to olefins. The pressure is within the range of from about 50 to about 2000 pounds per square inch and preferably of from about 500 to about 1000 pounds per square inch. The temperature is within the range of from about 800 F. to about 1200 F. and preferably within the range of from about 900 F. to about 1100 F. The low boiling portion of the raflinate is subjected to these pressures and temperatures for a time sufficient to convert a substantial portion of the parafiins to olefins and the exact time is dependent upon the particular temperature and pressure selected. At higher temperatures less time is necessary than at lower temperatures. The thermal treatment or thermal reforming is conducted in a thermal treating zone. The zone may be one reactor or two or more reactors in series. In a preferred method, the conversion zone is a thermal coil or thermal reforming coil in a heater so that the reactants may be more easily maintained at the conversion temperature. The actual residence time of a particular molecule in the thermal reforming zone usually is from about ten seconds to about five hundred seconds or more depending upon the temperature and pressure, as hereinbefore mentioned.

The effluent from the thermal reforming zone may be subjected to stabilization to separate the normally gaseous components therefrom, as is preferably performed on the eflluent from the catalytic reforming zone. The stabilized, thermally reformed fraction may be combined with one or more of the product streams of the process and, preferably, at least a portion of the stabilized, thermally reformed fraction is combined with at least a portion of the aromatic-rich hydrocarbon fraction from the separation zone. The mixture is a motor fuel of high octane number and excellent starting characteristics.

Additional features and advantages of my process will be apparent from the following description of the accompanying drawing which illustrates a particular method for conducting a gasoline upgrading operation in accordance with the present invention.

Referring now to the drawing a straight-run gasoline fraction having an initial boiling point of 200 F. and an end point of 400 F. is passed through line 1, is picked up valve 4 and line 5. A raffinate recycle stream in line 8,

prepared as hereinafter specified, and a hydrogen-rich gas stream in line 7 mix with the charge in line 5 and the mixture in line 6 is passed into heater 9 wherein the combined stream is heated to a temperature of 910 F. The heated combined stream is withdrawn from heater 9 by way of line 10 and passes into reforming reactor 11.

Reforming reactor 11 contains a bed of cylindrical catalyst of approximately A3 inch length and A; inch diameter containing 0.4% platinum, 0.5% combined fluorine, and 0.2% by weight of combined chlorine. The pressure in the reactor is 650 pounds per square inch, the weight hourly space velocity is 3.5 and the hydrogen to hydrocarbon mol ratio is 7 to 1. During the passage of the charge stock through reactor 11 the bulk of the naphthenes containing six or more carbon atoms per molecule are dehydrogenated to the corresponding aromatics and a portion of the paraffins are hydrocracked to lower boiling parafiins. Some isomerization of the paraffins also takes place, this reaction being of particular importance in the isomerization of normal hexane as this hydrocarbon is of relatively low octane number and is not readily dehydrocyclicized. The important octane number increasing reaction of dehydrocyclization also occurs in reactor 11 at these conditions. By this reaction a substantial portion of the parafiins are converted to aromatics. This reaction is extremely important in increasing the octane number of the paratfins which are recycled to the reforming reactor through line 8. The conditions in the reforming zone 11 or reactor 11 are such that there are substantially no olefinic substances produced. The efiiuent from reactor 11 passes through line 12, cooler 13, line 14, and into separator 15. Hydrogen is withdrawn from the top of separator 15 through line 16. Excess hydrogen may also be withdrawn through line 17 containing valve 18. At least a portion of the hydrogen in line 16 passes through line 19, is picked up by compressor 20 and discharged into line 7.

The liquid hydrocarbons, comprising the reformate and the bulk of the normally gaseous hydrocarbons produced in the process, are withdrawn from receiver 15 through line 21 and passed into fractionator or stabilizer 30. Normally gaseous hydrocarbons are removed overhead through line 31. In stabilizer 30 the normally gase ous material, which includes hydrogen, ammonia, hydrogen sulfide, and hydrocarbon gases containing from one to four carbon atoms per molecule, is separated from the hydrocarbon liquid comprising aromatic hydrocarbons and parafiinic hydrocarbons.

The gaseous material passes overhead through line 31 into cooler 32 wherein a portion of the material is condensecl and the entire stream passes through line 33 into receiver 34. In receiver 34 the liquid phase and the gas phase of the overhead material separate. The gases pass through line 41 from which they may be vented to the atomsphere or otherwise used. The stabilizer has heat provided thereto by reboiler 38 and connecting lines 37 and 39. The conditions in the stabilizer 30 are usually such that C and lighter components are removed as overhead; however, the gasoline therein may be cut deeper, that is C and/ or C hydrocarbons may be removed overhead through line 31. It is contemplated that the stabilizer 30 and receiver 34 will operate at a sufiicient pressure to liquefy at least a portion of the overhead material so that a liquid stream may be available to improve the separation in stabilizer 30. The liquid reflux passes from receiver 34 through line 35 into an upper portion of stabilizer 30. Liquid in receiver 34 may also be withdrawn through line 36.

The stabilizer bottoms, which as hereinbefore stated comprise substantially parafl'inic and aromatic hydrocarbons, are withdrawn through line 40 and introduced into a lower portion of extractor 50. In extractor 50 the hydrocarbon material rises and is countercurrently contacted at an elevated temperature in the liquid phase with a descending stream of a selective solvent. In this embodiment 98% diethylene glycol and 2% water is used as the solvent. The average temperature is 305 F. and the pressure is 150 p.s.i.g. Water is introduced through line 42 containing valve 43. The diethylene glycol enters the upper portion of extractor 50 through line 65. As hereinbefore mentioned, the Water is added to increase the selectivity of the solvent in line 65.

As a result of the countercurrent contact of the selective solvent and hydrocarbon stock, the aromatic hydrocarbons contained in the charged stock introduced through line 40 are selectively dissolved in the solvent, thereby forming an extract stream 52 containing the solvent and the bulk of the aromatic hydrocarbons and a predominantly parafiinic raffinate stream 51 containing the bulk of the paraffinic hydrocarbons and some of the higher boiling aromatics. The raffinate stream passes from the upper portion of extractor 50 through line 51 while the extract phase stream passes from the lower portion of extractor 50 through line 52.

The extract phase in line 52 is introduced to stripper 60 wherein the dissolved aromatic hydrocarbons and minor amounts of dissolved parafiins are separated from the selective solvent. The aromatic hydrocarbon stream along with some light paratfins passes overhead through line 61 and may be recovered as product or subjected to a further rectification or purification step. Heat is provided for the stripping operation by reboiler 63 and connecting lines 62 and 64. The solvent stream is taken from the bottom of stripper 60 through line 65 and is passed into the upper portion of extractor 50.

The rafi'inate stream in line 51 is introduced into fractionator 70. A portion of the stream in line 51 may be withdrawn as product through line 55 containing valve 56. A light fraction is removed overhead through line 71, passes through cooler 72, line 73, and into receiver 74. A portion of the liquid material in receiver 74 is used as reflux and is passed through line 75 into an upper portion of fractionator 70. Another portion of the liquid in receiver 74 is withdrawn through line 76 and introduced into thermal reformer 77. A portion of the stream in line 76 may be withdrawn through line 79 containing valve 79'. In another embodiment of the present invention, not herein illustrated, a light overhead fraction, preferably an isohexane and lighter fraction is removed from the upper portion of fractionator 70 and the light fraction to be charged to the thermal reformer 77 is withdrawn from an intermediate portion of the upper-half of the fractionator 70. A heavy fraction, that is a fraction boiling above about 400 F., is withdrawn from the bottom of fractionator 70 through line 83. Heat is provided for the fractionation by reboiler 81 and connecting lines 80 and 82. A heavy raffinate fraction is withdrawn near the bottom of fractionator 70 through line 8 and this heavy rafiinate fraction is recycled through line 8 and eventually passes through reforming reactor 11.

The light raflinate fraction in line 76 is introduced to thermal conversion zone 77. Thermal conversion zone 77 is herein illustrated as a heater in which tubes, or a coil is located. In the thermal heating zone 77, the light raflinate fraction is heated to an elevated temperature and the time, temperature, and pressure are maintained so as to produce a substantial amount of olefins. In the operation described, a temperature of 1050 F. and a pressure of 500 pounds per square inch are employed. At these conditions the average residence time of the charge stream is about one hundred seconds.

The resulting thermally reformed stream passes from thermal reforming zone 77 through line 78. The thermally reformed stream in line 78 may be stabilized to remove normally gaseous components therefrom, and the stabilized thermally reformed gasoline may be com- I 10 bined with other product streams and preferably is combined with product stream 61.

The following example is given to further illustrate my invention but is not given for the purpose of unduly limiting the generally broad scope of said invention.

Example A straight-run naphtha having an initial boiling point of 175 F. and an end point of 400 F. is reformed by passing the fraction through a catalytic reactor tube located in an electrically heated furnace. The tube is filled with a catalyst containing alumina, 0.4% platinum, and 0.5% fluorine. Hydrogen is also introduced into the reaction zone. A heavy raflinate fraction, prepared as hereinafter set forth, having an initial boiling point of 250 F. and an end point of 400 F. is also passed to the reaction zone along with the naphtha fraction and hydrogen. The reforming conditions maintained in the reactor are an average catalyst temperature of 885 F., a pressure of 600 pounds per square inch, a weight hourly space velocity of 3.0, and a hydrogen to hydro carbon mol ratio of 6:1.

The effluent from the reactor is stabilized in a fractionating column by removing C and a lighter component. The stabilized product is passed to a lower portion of an extraction column. The hydrocarbon liquid is pumped into the extraction column, rises and is countercurrently contacted with a stream of 98% diethylene glycol and 2% water. The extractor is maintained at a temperature of 300 F. and a 5:1 solvent to feed ratio. The pressure on the column is 100 pounds per square inch.

The extract phase is removed from the bottom of the extraction column and passed to a stripper in which the aromatics are separated from the solvent by a steam stripping operation. The rafiinate is removed from the top of the extractor and is passed to a fractionator. The raffinate is fractionated into three fractions: (1) i.b.p.- 250 F., (2) 250 F.-400 F., and (3) 400 F.e.p. The 250 F.-400 F. fraction is recycled direct to the reforming reactor. The i.b.p.250 P. fraction is passed to a thermal reactor maintained at 700 pounds per square inch and 1025 F. The efiluent from the thermal reactor is stabilized and analyzed. The thermally reformed gasoline contains a substantial amount of olefins and is higher in octane number than the charge to the thermal reformer. The stabilized thermally reformed gasoline is blended with the 400 F.e.p. fraction and with the aromatics separated from the stripper. The blend is a motor fuel of high octane number and excellent starting characteristics.

I claim as my invention:

1. A conversion process which comprises catalytically reforming a gasoline fraction, subjecting the reformed gasoline to solvent extraction to form an aromatic extract and a paraffinic raflinate, fractionating the rafiinate and separating therefrom a heavy rafiinate fraction having an initial boiling point in the range of about 225 325 F. and a light raffinate fraction having an end boiling point in the range of about 225-325 F., subjecting the light raffinate fraction to thermal non-catalytic reforming to convert paraffins to olefins, and returning the heavy rafilnate fraction to the catalytic reforming step.

2. A conversion process which comprises catalytically reforming a gasoline fraction, subjecting the reformed gasoline to solvent extraction to form an aromatic extract and a paraffinic raflinate, fractionating the raflinate and separating therefrom a heavy rafiinate fraction having an initial boiling point in the range of about 225 325 F. and a light raflinate fraction having an end boiling point in the range of about 225-325 F., returning the heavy rafiinate fraction to the catalytic reforming step, subjecting the light raffinate fraction to thermal non-catalytic reforming to convert paraffins to olefins 11 12 and commiugling resultant olefins with at least a portion 2,659,692 Haensel et al Nov. 17, 1953 of said aromatic extract. 2,697,684 Hemminger et a1. Dec. 21, 1954 2,853,437 Haensel Sept. 23, 1958 References Cited in the file of this patent UNITED STATES PATENTS 5 OTHER REFERENCES Laying et a1. Dec. 8, 1942 Relation of Properties to Molecular Structure for Sensel et al. June 6, 1944 Petroleum Hydrocarbons, by Cecil E. Boord, Progress Goldsby Jan. 1, 1946 in Petroleum Technology, Amer. Chem. Soc., Washing- Welty Dec. 6, 1949 ton, DO, 1951, page 365 and table IX, page 368. 

1. A CONVERSION PROCESS WHICH COMPRISES CATALYTICALLY REFORMING A GASOLINE FRACTION, SUBJECTING THE REFORMED GASOLINE TO SOLVENT EXTRACTION TO FORM AN AROMATIC EXTRACT AND A PARAFFINIC RAFFINATE, FRACTIONING THE RAFFINATE AND SEPARATING THEREFROM A HEAVY RAFFINATE FRACTION HAVING AN INITIAL BOILING POINT IN THE RANGE OF ABOUT 225* 325* F. AND A LIGHT RAFFINATE FRACTION HAVING AN END BOILING POINT IN THE RANGE OF ABOUT 225*-325*F., SUB JECTING THE LIGHT RAFFINATE FRACTION TO THERMAL NON-CATALYTIC REFORMING TO CONVERT PARAFFINS TO OLEFINS, AND RETURNING THE HEAVY RAFFINATE FRACTION TO THE CATALYTIC REFORMING STEP. 